[skyking]

something like that indeed.
Example:
XPS foam can be had in varying densities.
The common stuff is 1.5 Lb/cu. ft.
You can make a 2" thick lid, 2' high by 14' long by 6.5' wide with 172 sq foot of XPS.
172 x .166 = 28.5 cu. ft. x 1.5 = ~43 pounds of foam.
Add a generous 50 yards of 6 oz glass and a couple of gallons of epoxy and paint and this lid still weighs in under 100 pounds.
Unlatch, step inside and lift one end and then the other. Make a tripping catch to keep it up there until you can insert a couple of pins.
I'm not fond of fabric when it sweats and drips, mildews, has to be dried out after a soggy trip. Been there done that.
This type of lid will have R10 insulation as well as strength.